In adhesion of a macromolecular material to a metal, as compared with the adhesion to a base metal such as cobalt, chromium, nickel, titanium, iron, and copper, or an alloy thereof, the adhesion to a chemically stable noble metal such as gold, platinum, and palladium, or a noble metal alloy containing such a noble metal as a major component is extremely difficult, and hence, the present situation is that any thoroughly satisfactory adhesion technologies have not yet been established.
As attempts for improving the adhesive properties to a noble metal, there have been proposed some methods for applying a primer onto a metal surface as an adherend, a method for sandblasting to physically roughing a metal surface as an adherend, a method for plating a metal surface as an adherend with tin, a method for subjecting a metal surface as an adherend to oxidation processing, and the like.
Of these methods, the method for applying a primer onto a metal surface as an adherend is simplest, and examples of such method include a method in which 6-(4-vinylbenzyl-n-propyl)amino-1,3,5-triazine-2,4-dithione (hereinafter referred to as "VBATDT") is used as a primer to be applied, as disclosed in Japanese Patent Laid-Open No. 64-83254, and method in which a polymerizable monomer containing a thiophosphoric acid group therein is used as a primer to be applied, as disclosed in Japanese Patent Laid-Open No. 1-138282 and Japanese Patent Laid-Open No. 3-310122.
Although many of the above-described conventional technologies are admitted to have an effect for increasing the adhesive strength under dry conditions, they involve such a defect that the water resistance or durability is poor.
Of the methods for applying a primer onto a metal surface as an adherend, the method of using VBATDT can not be said to be sufficient in an effect for improving the adhesive properties to any of base metals or noble metals; and while the method of using a monomer containing a thiophosphoric acid group therein is admitted to have an effect for improving the adhesive properties, this method not only has a problem in storage or handling of the primer, because the substance itself is unstable, but also involves such a problem that the water resistance or durability is inferior.